1. Field of the Invention
Embodiments of the invention generally relate to the formation of metal nitride barrier layers and conductive metal layers deposited thereon, and more particularly, to titanium nitride barrier layers and aluminum layers deposited thereon.
2. Description of the Related Art
In the manufacture of integrated circuits, barrier layers are often used to inhibit the diffusion of metals and other impurities into regions underlying such barrier layers. These underlying regions may include transistor gates, capacitor dielectric, semiconductor substrates, metal lines, as well as many other structures that appear in integrated circuits. For the current submicron generation of semiconductor devices, any microscopic reaction at an interface between interconnection layers can cause degradation of the resulting integrated circuits (e.g., increase the resistivity of the interconnection layers). Consequently, barrier layers have become a critical component for improving the reliability of interconnect metallization schemes.
Compounds of refractory metals such as, for example, nitrides, borides, silicides, and carbides have been suggested as diffusion barriers because of their chemical inertness and low resistivities (e.g., resistivities typically less than about 500 μΩ-cm). In particular, refractory metal nitrides, such as, for example, titanium nitride have been suggested for use as a barrier material since layers formed thereof generally have low resistivities and are chemically stable at high temperatures.
Refractory metal nitride barrier layers may be formed using chemical vapor deposition (CVD), atomic layer deposition (ALD), or physical vapor deposition (PVD) processes. During a CVD or ALD process, a titanium precursor may be reacted with a nitrogen precursor (e.g., TiCl4 and NH3) to form titanium nitride layer. However, CVD or ALD processes may require high deposition temperatures (e.g., >600° C.) to form a typical titanium nitride layer, which may affect other material layers that are in contact with the metal nitride barrier layers. For example, metal nitride barrier layers are often deposited onto buried semiconductor junctions. At high temperatures dopants in the semiconductor junctions may diffuse out of the buried junctions, potentially changing the characteristics thereof.
Additionally, when chlorine-based chemistries are used to form the metal nitride barrier layers during a CVD or ALD process, such nitride layers typically contain chlorine contaminants therein. A high chlorine concentration is undesirable because chlorine may migrate from the metal nitride barrier layer into adjacent material layers (e.g., interconnection layers) which can increase the contact resistance of such layers, potentially changing the characteristics of integrated circuits made therefrom. Alternatively, organometallic precursors (e.g., tetrakis(dialkylamido) titanium compounds) may be used during a CVD or ALD process. However, the metal nitride barrier layers formed from an organometallic precursor often contain high levels of carbon, which increases the resistivity of the material.
Other problems that occur while manufacturing electronic devices is due to the need for smaller structures, especially for apertures and vias, which are approaching widths of 0.12 μm and smaller. These high aspect ratio structures have complicated surfaces to deposit barrier layers on, and also small vias that need to be filled with conductive materials, such as aluminum. The reliability of an aluminum plug is lost if gaps are formed within the vias while being filled with aluminum.
Therefore, a need exists for reliable metal nitride barrier layers used in integrated circuit fabrication, particularly desirable is titanium nitride barrier layers. Also, a need exist for a process to fill high aspect ratio structures with conductive materials, preferably, aluminum.